How Illinois Nuclear Fleet Weathered Record Heat While Powering Millions

When Chicago sweltered through its hottest summer on record, nuclear plants in Illinois became the silent workhorses keeping the lights on. Six reactor facilities operated at near-maximum capacity throughout June, July, and August, generating carbon-free electricity around the clock for more than 11 million homes and businesses across the region.

The reliability numbers tell the story: Exelon Generation’s nuclear plants in Illinois achieved a 98.9 percent uptime rate last summer—meaning they were producing power on demand when demand mattered most. During peak heat events, hospitals, data centers, and emergency services depended on this steady output. Had fossil fuel plants filled the gap instead, the carbon emissions would have been substantial.

The Operational Reality Behind the Numbers

What outsiders don’t see is the preparation work. Months before summer heat arrives, operators and maintenance teams at all six sites conduct systematic inspections of backup generators, cooling systems, and spare equipment. This spring, crews tested and repaired critical infrastructure across the Illinois nuclear sites to ensure zero failures when temperatures climbed into record territory.

Over 4,700 full-time employees work across these facilities. Shane Marik, Senior Vice President for Midwest Operations at Exelon Generation, noted that “our nuclear facilities are among the most reliable power plants in the country,” a designation backed by industry efficiency ratings that track uptime and performance across competing technologies.

Why This Matters for Energy Policy

Nuclear plants in Illinois now face an uncertain future. Exelon Generation announced the retirement of Byron and Dresden facilities by 2021, plants that together employ 1,500 workers and supply 30 percent of the state’s carbon-free energy. The closures highlight a market challenge: despite perfect operational performance, these plants struggle against revenue headwinds in competitive power markets.

The timing is significant. Illinois aims for 100 percent clean energy, a goal that becomes harder to reach if carbon-neutral capacity shrinks. The summer data proves the plants can handle extreme demand; the question now is whether policy and market mechanisms will allow them to continue operating.

Exelon Generation operates the largest zero-carbon nuclear fleet in the United States, with more than 18,700 megawatts of capacity across 21 reactors at 12 facilities spanning Illinois, Maryland, New York, and Pennsylvania. The company also runs wind, solar, and hydroelectric assets, generating power for over 20 million homes and businesses nationally.